Hi
Welcome to the platform.
There are countless tools, you can find a lot of them (but not all of them) by clicking the menu icon in the top right corner, and then clicking the 'SteemIt app center'.

The ones I use most are:

• https://steemd.com/@yourusername - to check voting power
• https://steemworld.org/@yourusername - to check voting power and see loads of other stats about your account
• http://steem.supply/@yourusername - to check how much money is coming your way
• https://busy.org to write posts (they have a better editor)
• http://www.steemshare.com to bookmark posts
• http://www.steemreports.com/ for loads of info about your account

As a newbie, I would definitely download the following extensions:

• SteemIt More Info: https://steemit.com/steemdev/@armandocat/steemit-more-info-1-5-chrome-extension-firefox-extension

• Steem Toolbar: https://steemit.com/steemtoolbar/@arcange/steemtoolbar-google-chrome-extension

• SteemPlus https://steemit.com/utopian-io/@steem-plus/steemplus-2-4-utopian-1up-is-here

If you want to upload videos, use https://d.tube/

If you want to use SteemIt Twitter style: https://zappl.com/Home

If you want to post funny memes and stuff: https://www.dmania.lol/

Instagram style: https://steepshot.io/

Sound: https://dsound.audio/

And there are hundreds more.. ;0)